The present invention relates to electric machines and, more specifically, to winding arrangements for electric machines.
Many electric machines employ stators that have a core with a plurality of axially extending slots to receive one or more windings. Each winding is formed out of a continuous electrical conductor that extends through many of the stator slots with end loop portions connecting the winding segments disposed in the stator slots. The end loops extend beyond the axial ends of the stator core. The two opposing ends of the winding are connected to an appropriate component of the electric machine which may differ depending upon the design of the electric machine.
For many electric machines, such as those having a wye-configuration, one end of the winding will be a phase lead that is connected to an electrical source or load with the other end of the winding being connected to a neutral connection. The two ends of the winding generally extend from the same axial end of the stator. Many windings also include a reversing loop at the midpoint of the winding. Generally, each end loop will connect slot segments disposed in different layers, a conventional reversing end loop, however, connects two slot segments that are in the same layer. The winding may also have an electrical connection at this midpoint of the winding, for example, the winding may have an appropriate connection to provide either a series configuration or a parallel configuration. The reversing loop and connection, e.g., series connection, are generally also located at the same axial end of the stator as the two ends of the winding. These various features of the windings can be difficult to accommodate in the limited space available at the axial end of the stator. Multiple phase electric machines, e.g., three phase electric machines, will include at least the same number of windings as there are phases with each winding presenting such spatial difficulties.
FIG. 1 presents one phase of a conventional winding diagram. This diagram depicts a winding 20 wherein each slot holds two layers of the winding. The two layers are at different radial distances from the central axis but lie on a common radial line extending outwardly from the central axis. In this diagram, the winding is depicted in both solid lines and dashed lines. The use of a solid line designates that the winding is positioned in a first layer while the dashed line designates that the winding is positioned in a second layer. Circles 22 represent welds where the two hairpin wire segments have been welded together. One end 24 of winding 20 is a phase lead which would be connected to a rectifier or other component. The opposite end 26 of winding 20 is connected to a neutral connection 28. A reversing loop 30 is located at the midpoint of winding 20 and forms a series connection between the two halves of winding 20. As can be seen in this diagram, both the neutral connection 28 and reversing loop 30 are located in the same layer. This requires that either the neutral connector 28 or reversing loop 30 be axially displaced to spatially accommodate both of these structures.
FIG. 2 is a schematic winding diagram illustrating the use of three windings 20 wherein each of the windings 20 have the same configuration as depicted in FIG. 1. Such an arrangement would be suitable for a three phase electric machine. As can be understood with reference to FIG. 2, each winding does not have a segment in each slot of the stator core. FIG. 2 illustrates how neutral connection 28 is used to connect the neutral lead 26 of each of the three different phases together in an electric machine having a wye configuration. Those having ordinary skill in the art will understand the arrangement and functioning of the windings 20 depicted in FIG. 2.
For some electric machine designs, the spatial conflict created by the reversing loop and neutral connection being in the same layer presents a significant problem. For example, electric machines utilizing what are commonly referred to as large “hairpins” to form the stator windings may be encounter spatial conflicts at the axial ends of the stator. Large hairpins, when used in the context of stator windings, generally refer to wire with a cross sectional area of 4 mm2 or greater. Such hairpins typically have a generally U-shape with a central end loop section and two legs. The two legs are inserted through slots in the stator and then are welded to adjacent hairpin legs at one end of the stator to thereby form a continuous winding from a plurality of hairpins.
Such windings, and their various features, must fit into a spatial envelope that is commonly defined by 1) the rotor and rotor fan corresponding to the internal diameter of the stator; 2) the housing corresponding to the outer diameter of the housing; and 3) the housing end surface disposed axially beyond the end turns of the winding.
Several methods have been used to address the spatial conflicts that arise at this location within the electric machine. For example, U.S. Pat. No. 8,716,910 B2, which is hereby incorporated herein by reference, discloses an electric machine wherein the windings include jumper segments 32 that extend into the inner cylindrical space defined by the stator. This arrangement is depicted in FIG. 4 and works well for electric machines having an external fan or no fan at all. However, the position of the jumper 32 can conflict with the use of an internal fan coupled with the rotor and located within the cylindrical space defined by the internal diameter 34 of the stator core 36.
Another known approach to addressing these spatial conflicts is employed in alternators manufactured by Prestolite Electric Inc. headquarted in Novi, Michigan and which markets products under both the Prestolite Electric and Leece-Neville brand names. In this approach, depicted in FIG. 3, at one axial end of the stator, one end 38 of the winding 40 extends to form the phase lead and a reversing loop 42 is present and includes a series connection. The opposite end of the winding 44 is coupled with a neutral connection 46. Instead of having the neutral connection 46 at the same axial end of the stator as the phase lead 38, the neutral connection 46 is located at the opposite axial end of the stator. By placing the neutral connection at the opposite axial end, the spatial constraints are relieved. This arrangement, however, requires that, for one slot, one pass of the winding is omitted. For a stator winding having two layers, this will result in one slot that has only half filled by the winding. This half empty slot reduces the output of the electric machine and can generate magnetic noise during operation of the electric machine.
Further improvements which alleviate the spatial constraints present at the axial ends of electric machines are desirable.